The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Automatic transmissions use a fluid clutch known as a torque converter to transfer engine torque from the engine to the transmission. The torque converter operates through hydraulic force provided by pressurized fluid from the automatic transmission. The torque converter multiplies engine torque and directs it through the transmission.
A conventional torque converter includes a sealed chamber filled with hydraulic fluid. The chamber includes a pump (or impeller) driven by the engine, a turbine connected to an output shaft, and a stator that provides torque multiplication. A torque converter is said to “slip” when the impeller speed and the turbine speed are not equivalent. Some converters incorporate a lockup mechanism such as a mechanical clutch that engages at cruising speeds to physically link the impeller with the turbine. The physical link causes the impeller and the turbine to rotate at the same or near the same speed, thereby reducing or eliminating slip. The clutch is applied and released via fluid supplied through a hollow shaft at the center axis of the rotating converter assembly.
In some applications, the engine may employ a deceleration fuel cutoff device that is capable of operating the engine in a deceleration fuel cutoff (DFCO) mode. Operating in a DFCO mode is desirable during overrun conditions (i.e., going down a hill) or in city traffic, as well as for engine speed limitation purposes. Operation in the DFCO mode contributes to improved fuel economy.
In order to enter the DFCO mode, it is desirable for the torque converter clutch to be applied. This reverses the transfer of torque. More specifically, the applied clutch allows torque to be transferred from rotating drive wheels back to the engine crankshaft when the vehicle coasts. If the slip across the torque converter is too high or too low prior to entering the DFCO mode, the application of the torque converter clutch may be delayed or may not occur at all. Hence, delaying or preventing the engine from operating in the DFCO mode and thus, impacting fuel economy.